#1290 Convert Binary Number ina a Linked List to Integer.java

//https://leetcode.com/problems/convert-binary-number-in-a-linked-list-to-integer/
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public int getDecimalValue(ListNode head) {
        return helper(head,0);
    }
    public int helper(ListNode head, int n) {
        if(head == null) return n;
        n = n * 2 +head.val;
        return helper(head.next,n);
    }
}